The present invention concerns a lighting unit having a light source and having a wavelength-dependent filter device with a selectively transmissive filter and/or a selectively reflective mirror reflector in order, for the purpose of emphasizing the body color of an object to be illuminated, to filter out color components of the light coming from the lamp whose color locus on the chromaticity diagram is located opposite the color locus of the body color that is to be emphasized on a connecting line passing through the achromatic point (complementary color).
A lighting unit of this kind is known from DE 35 158 879 C1. This lighting unit possesses a filter device in order, for the purpose of emphasizing the xe2x80x9cwarmxe2x80x9d body colors orange, red, and purple, to filter out the corresponding complementary colors in the spectral region from 480 to 570 nm. Filtration in this relatively narrow spectral region results in filter transmission curves with steep filter edges. In addition, not only is the body color that is to be emphasized indeed emphasized, but the color of the light itself is also greatly modified, so that an optionally white surrounding area is undesirably given a reddish tint.
The narrow-band filters that are used are usually manufactured as interference filters, and their function requires a plurality of interference layers. While the use of such filters in lighting units whose lamps radiate a continuous light spectrum, for example halogen lamps, is relatively unproblematic, the use of a filtration arrangement of this kind is problematic when the lamps used are ones that generate a line spectrum. Especially when using a high-pressure sodium vapor lamp with improved color reproduction, whose light spectrum is intended to emphasize red by way of a filter arrangement of this kind, the transmission minimum of the filter curve coincides with a steep edge in the light spectrum of this lamp, so that tolerances in filter manufacture, which are un-avoidable, have a very pronounced effect.
A further problem is the fact that the effect of such interference filters depends to a great degree on the angle of the incoming light.
It is therefore the object of the present invention to configure a lighting unit of the kind cited initially in such a way that the desired emphasis of a body color is associated with only minor modification of the light color, and the filter effect is insensitive to production tolerances both of the lamps used and of the filter device. The intention in particular is to make possible, without difficulty, the use of lamps that radiate a line spectrum, and to decrease the angular dependence of the filter device.
According to the present invention, this object is achieved in that the filter device additionally filters out a portion of the color component of the same body color that is to be emphasized.
The invention is thus based on the idea of filtering out not only the colors complementary to a body color that is to be emphasized, but also a portion of the same body color that is to be emphasized. If the body color red is to be emphasized, for example, the color components of the complementary colors are filtered out in conventional fashion, and according to the present invention reddish color components in the region from 660 to 780 nm are additionally filtered out as well. The result of filtering out these reddish color components is that the light color is influenced in such a way that a white surrounding area has less of a reddish tint or none at all, i.e. the white background remains substantially white. The fact that these color components are filtered out has almost no influence on the emphasis of the body color, since these spectral components that are additionally filtered out are located in that region of the photopic response curve of the human eye in which the eye possesses little sensitivity, so that absorption or reflection losses in terms of light attenuation by the filter device are imperceptible.
When lamps with a continuous light spectrum are used, the color components having wavelengths substantially between 480 nm and 570 nm can be filtered out, in known fashion, in order to emphasize xe2x80x9cwarmxe2x80x9d body colors. When a lamp with a highly inhomogeneous line spectrum, for example a high-pressure sodium vapor lamp, is to be used, then according to the present invention a filter device with a comparatively less narrow-band reflection or absorption characteristic is selected, for example a filter that is effective in the wavelength region from 500 nm to 620 nm. In addition, the filter device can be selected so that the absorption or reflection in the wavelength region from 480 to 620 nm is a maximum of 70%. The result of these actions is that the filter transmission curve has less-steep filter edges and shallower troughs, so that filter manufacturing tolerances have less of an effect.